Wind energy installations of the type mentioned initially have variable-pitch rotor blades whose pitch angle with respect to the incident wind can be varied. Pitch systems such as these allow two different functionalities, specifically on the one hand variable rotation-speed operation, and on the other hand allow the wind energy installation to be shut down. The latter is done by moving the rotor blades to a feathered position in which they are no longer caused to rotate by the wind. The latter function is actually particularly important since it acts as a braking function. This is a particularly safety-critical aspect for the wind energy installation. In order to make it possible to ensure that the wind energy installation can be shut down via the pitch control, even if the electrical power supply to the wind energy installation fails, dedicated rechargeable-battery systems are generally provided for the pitch device. These ensure that electrical power is supplied to the pitch device even in the event of power supply system failure. Conventional rechargeable batteries or else capacitors with a particularly high capacitance (for example ultra caps) are used as energy stores. Absolutely independently of the precise design used for the rechargeable batteries, they are nevertheless subject to the same disadvantage that these are parts which are subject to wear. In order to safely prevent the failure of the pitch device because of a possibly defective rechargeable battery, because of the safety-critical functionality, the rechargeable batteries are checked at regular time intervals. Various methods have become known in the prior art for this purpose.
DE 10 2005 030 709 discloses the life of the rechargeable batteries being lengthened by optimizing the load and charging processes, by using current-limiting measures, monitoring the temperature of the rechargeable batteries, and measuring the terminal voltage of the individual rechargeable batteries.